Theres several ways. I usually use my cutlass. However, a dremel with a cutting wheel, or even a razor blade are both viable alternatives.
And if you do *Can'tSayThisOnTV* up, its not impossible to fix. Bondo, ABS cement, glazing putty, epoxy, and even hotglue (see: SS, circa 2006) are all usable for fixing cracks and such.